1. Field of the Invention
The present invention relates to filters for removal of soluble and colloidal, non-soluble particles in a fluid. Specifically, the present invention relates to the removal of soluble and insoluble lead from a fluid, and more specifically, to the removal of soluble and insoluble lead from high pH fluid using fibrillated nanofibers as one of the filter media.
2. Description of Related Art
Certain water treatment applications are characterized by the need to remove both dissolved and suspended or colloidal materials. Although it has been used in numerous consumer products, lead is a toxic metal now known to be harmful to human health if inhaled or ingested. Important sources of lead exposure include: ambient air, soil and dust (both inside and outside the home), food (which can be contaminated by lead in the air or in food containers), and water (from the corrosion of plumbing). Materials such as ion exchange resins and reverse osmosis membranes effectively reduce or fully remove dissolved ionic species. Particulate lead at high pH exists primarily as colloidal lead carbonates. These colloidal particulate solids can be physically removed if the filter media provides for a fine enough mesh that can also accommodate pressure differentials.
Standards have been developed and promulgated to regulate the amount of contaminants allowed in drinking water. For example, one such standard is NSF/ANSI 53, entitled “DRINKING WATER TREATMENT UNITS—HEALTH EFFECT.” This is an NSF International Standard and an American National Standard for establishing minimum requirements for materials, design, construction, and performance of point-of-use and point-of-entry drinking water treatment systems that are designed to reduce specific health-related contaminants in public or private water supplies. This standard, as well as other related standards and protocols, governs the amount of contaminants in drinking water, including lead, governs testing protocols for removal of those contaminants which provides a benchmark for the efficacy of water filters designed to remove or reduce such contaminants.
For example, pursuant to the NSF requirement, the influent challenge for total lead is 0.15 mg/L or 150 ppb of which 30% or 50 ppb is total particulate lead, and 20% of the total particulate lead or 10 ppb is fine lead between 0.1 and 1.2 microns in size. The maximum effluent lead concentration is 0.010 mg/L. The total lead requirement is applicable for lead pH 6.5 and lead pH 8.5 reduction testing. The lead particulate and fine lead values are of the greatest concern lead pH 8.5 testing only. A filter designed to specifications of the present invention is capable of meeting the NSF or other similar standard challenge requirements for the reduction of lead in drinking water.
For many years fibers such as cellulose have been utilized as filter aids to improve flow and reduce differential pressure across the surface of a bed or precoat. Fibers dramatically improve removal of colloidal materials, especially when used in conjunction with charged materials such as ion exchange resins. U.S. Pat. No. 4,190,532 issued to Halbfoster on Feb. 26, 1980, entitled “CHARGED FILTER AID MATERIAL AND ION EXCHANGE BED,” first described the synergistic effects of combining charged ion exchange resins and charged filter aid such as treated cellulose fiber. The invention embodied in this patent is now widely used commercially in applications such as treating high quality condensate water in power plants.
A more recent patent, U.S. Pat. No. 6,872,311 issued to Koslow on Mar. 29, 2005, entitled “NANOFIBER FILTER MEDIA,” describes the use of nanofibers as an enhanced filtration medium. The patent teaches that a physical process called fibrillation enhances the performance of standard filter media such as cellulose fiber. Moreover, this patent also teaches a process for making an improved air filter medium with the incorporation of nanofibers. This process has also been commercialized for filtration purposes in combination with activated carbon.
There are a number of independent agencies, such as NSF International, UL, and WQA, to name a few, that evaluate and certify the performance of filtering devices that remove lead from drinking water. Generally, their seal of approval appears on the device and product packaging. New testing criteria from these agencies require the removal of lead in high pH fluid.